Tire and Wheel Measurements
Wheel and tire measurements are often used colloquially with the assumption that their measurements are understood by the audience. However, wheel and tire code is presented in a very unique manner that needs a key to be deciphered. Bolt Circle Measurements The bolt circle measurement is perhaps the most important measurement of a wheel. It describes the diameter of the circle in which the bolts holes are arranged. These, of course, must match the bolts on your vehicle. Below are the measurements for the various generations of Honda Preludes. First through Third generation Honda Prelude 1979-1991: 4x100m / 12x1.5 Lug-nut / 56.10mm Bore Fourth generation Honda Prelude 1992-1996: 4x114.3mm / 12x15 Lug-nut / 64.10mm Bore Fifth generation Honda Prelude 1997-2001: 5x114.3mm / 12x1.5 Lug-nut / 64.10mm Bore Tire Measurements Tire measurements contain two different units of measurement and one number that isn't an actual measurement, but a ratio. Tire measurements usually appear like this in our forums: XXX/YY/ZZ (215/40/17 would be an example). XXX is a measurement in millimeters of the widest part of the tire, which is the bulge in the sidewalls. This is known as the "Section Width". YY is the ratio of the height of the sidewall to the section width (XXX). This is known as the "Section Height". This is not a static measurement, as a 40% ratio with a 215mm section width would be 86mm, whereas a 40% ratio with a 230mm section width would be 92mm. ZZ is a measurement in inches of the inner diameter of the tire, this tells you the size of wheel it will fit (at least as far as the diameter is concerned. So 215/40/17 would mean a tire that is 215mm wide at the sidewalls, with a sidewall height that is 40% of the sidewall width (86mm in this case) and has a 17in hole in the middle to fit around the rim. Wheel Measurements Wheel measurements are much easier. They usually appear in our forums in the following format: AAxB.B +CC (17x8.5 +35 would be an example). AA is a measurement in inches of the diameter of the wheel. It needs to be the same as the ZZ measurement of your tires and vice versa. B.B is a measurement in inches of the rim width of the wheel. This needs to be roughly similar to the section width of your tires. Generally, it should be slightly smaller. (You'll need to convert from millimeters to inches.) +/-CC is a measurement in millimeters of the offset of the wheel, or the distance between the center line of the wheel and the face of the wheel that actually bolts onto the hub. A positive offset moves the face from the center line of the wheel towards the outside of the car, creating room inside the wheel for brake calipers while pulling the tires inward from the outside of the car. A negative offset moves the face of the wheel towards the inside of the car, pushing the tires outwards.